AVS1997 Session TF+VM-TuM: Hard Coatings

Tuesday, October 21, 1997 8:20 AM in Room B3/4

Tuesday Morning

Start	Invited?	Item
8:20 AM		TF+VM-TuM-1 Film Growth of Nanostructured C-N/TiN_x Mulilayers Reactively Sputtered in Pure Nitrogen. H. Jensen (University of Aarhus, Denmark); J. Sobota (Institute of Scientific Instruments, Czech Republic); G. Sorensen (University of Aarhus, Denmark) The present communication will report on nanostructured C-N/TiN_x deposited when two cathodes of carbon and titanium were operating concurrently in pure nitrogen in the side by side configuration. Experimental parameters of relevance for the pseudomorfic growth of the carbon nitride multilayer system such as nitrogen pressure and rotation speed of the substrate holder, i.e. bilayer thickness, will be discussed. The composite coatings, typically 2-3 micrometer thick, were deposited at a pressure ranging from 0.2 to 1 Pa, and it will be discussed whether it will be possible obtain an appropriate seeding for the C-N system simply by nitrogen sputtering of titanium. Various substrates such as silicon, high speed steel and WC were used, and the friction coefficient for a Si₃N₄ ball was measured in a reciprocating ball on disk tribometer was measured, and material transfer in the contact will be reported. The adhesion to the substrate was measured with a LSRH Revetest acoustic emission scratch tester and compared with previous results for C-N/TiN_x multilayer coatings reactively sputtered in argon/nitrogen mixtures. Also dynamic impact testing of nanostructured multilayers has been attempted. The perspectives of simple seeding systems containing titanium will be discussed also in the stationary deposition set up.
8:40 AM		TF+VM-TuM-2 Electrical and Optical Properties of Magnetron Sputtered Boride and Silicide Coatings P.M. Martin, D.C. Stewart, W.D. Bennett, J.W. Johnston (Pacific Northwest National Laboratory); E. Savrun (Sienna Technologies) The electrical and optical properties of several thin-film boride and silicide coatings were determined. All coatings were deposited by magnetron sputtering techniques. TiB₂, ZrB₂, CrB₂, TaB₂, NbB₂, VB₂, and LaB₆ coatings were deposited using sintered and pressed powder stoichiometric targets. A range of Si/W compositions with values from 0.50 to 9 to was deposited by cosputtering the refractory metal and Si targets. These materials had Knoop hardnesses ranging from 2000 to 4500, and melting temperatures ranging from 2500 to 3200 °C, which make them attractive for optical applications in severe environments. They had no known chemical etchants. Reflectance and transmittance were measured from 0.4 to 20 µm wavelengths. Reflectance of boride coatings at visible wavelengths ranged from 0.32 to 0.55, and increased monotonically to values between 0.90 and 0.94 in the LWIR. Infrared ellipsometer measurements made on ZrB₂ coatings found n and k to be between 6 and 8 at 5 µm wavelength. The boride coatings displayed electrical properties characteristic of semimetals, with electrical resistivity ranging from 200 to 700 µω.cm. Transmittance and reflectance of the silicide coatings depended on Si/metal ratio, and ranged from that of the metal to below that of Si. Electrical resistivity of these coatings increased from 60 µω.cm for Si/W of 0.54 to 900 µω.cm for Si/W of 9. The infrared reflectance also increased with decreasing Si/W values, showing a minimum of 0.445 for Si/W of 9 (the reflectance of Si was 0.51) and a maximum of 0.70 for Si/W of 2.1.
9:00 AM		TF+VM-TuM-3 Diffusion Bonding of Steel to Titanium to produce Hard Wearing Surface Layers. S.C. Church, R.K. Wild (University of Bristol, United Kingdom) Titanium is a light, strong alloy used extensively in applications where weight saving is important. However, the surface does not resist abrasion with the result that it cannot be used in applications wear the component must resist wear, such as gear components. Attempts to harden the surface, such as nitriding, have met with limited success. To produce a light component with a hard wearing surface, steel has been diffusion bonded to titanium. This has been done using a bench top diffusion bonding rig, operating in vacuum at temperatures up to 1273K, which has been designed and built in house. Computer control allows predetermined stresses and strains to be carefully controlled. The diffusion bond has been achieved both without interlayers and with up to three interlayers of elements such as copper, vanadium and nickel. Results will be presented showing the effect of stress, strain and interlayers on the strength of the diffusion bond. In many cases bond strengths approaching that of the bulk matrix have been achieved. The microstructure of the interfaces have been characterised using optical metallography, scanning electron microscopy, transmission electron microscopy and Auger electron microscopy.
9:20 AM		TF+VM-TuM-4 Frictional and Related Surface Chemical Properties of Carbide and Nitride Hard Coating Materials S.V. Didziulis, P.P. Frantz (The Aerospace Corporation); S. Lee, P.B. Merrill, S.S. Perry (University of Houston) Metal carbides and metal nitrides are becoming increasingly important as protective coatings in wear environments. In such environments, frictional and surface chemical properties also are closely related to the mechanical performance of the interface. In this study, the frictional properties of titanium carbide, titanium nitride, and vanadium carbide have been measured on a microscopic scale with atomic force microscopy and on macroscopic scale with pin on disk measurements. Frictional properties have been measured as a function of relative humidity and counterface material. These properties have been further correlated with the specific chemical composition of the surface and the nature of different surface reactivities.
9:40 AM	Invited	TF+VM-TuM-5 Recent Developments in the Design, Deposition, and Processing of Hard Coatings J.S. Zabinski (Wright Laboratory, Materials Directorate, USAF); A.A. Voevodin, J.J. Nainaparampil (Systran, Wright Laboratory, Materials Directorate) Hard coatings have been studied for many years as a means to reduce wear, provide protection against corrosion, and increase performance. During the early years, hard coatings research was directed on single phase, single layer, binary materials. This work lead to an understanding of the effects of deposition conditions on coating properties and performance. Many of these types of materials were successfully employed commercially. The next generation of materials includes multilayer, multicomponent, functionally gradient, and composite coatings. These types of coatings can be viewed as a system where the focus is location dependent. For example, at the substrate interface the focus is typically adhesion while in the mid-region , load support and toughness may be targeted, and finally friction may be the most critical surface characteristic. Much effort has been focused on achieving high hardness by superlattice and composite designs. While hardness is important, a combination of hardness, toughness, and low friction will produce the best coating performance. In this paper, coating designs (e.g., functionally gradient, multilayer, and nanocomposites) for achieving a balance of properties are discussed. Deposition techniques that permit the fabrication of designed coatings will be shown (e.g., magnetron sputter assisted pulsed laser deposition and ion beam assisted deposition). Emphasis will be on the control of energy through substrate bias, ion beam assist, sample/target geometry, and degree of plasma ionization. By strategically controlling energy to the growing interface, coating chemistry and microstructure can be adjusted in a predictable fashion. This, in turn, permits optimization of overall coating performance. These concepts will be demonstrated in the production of superhard DLC, functionally gradient/multilayer Ti/TiC/DLC and Si/SiC, and ion beam assisted pulsed laser deposited Al₂O₃. In all cases, control of the coating architecture provided coatings with unique and superior properties.
10:20 AM		TF+VM-TuM-7 Structure, Mechanical and Tribological Properties of Sputtered and Electron-Beam Evaporated TiAlBN PVD hard Coatings C. Rebholz, A. Leyland (University of Hull, United Kingdom); J.M. Schneider (Northwestern University); S.L. Rohde (University of Nebraska); A. Matthews (University of Hull, United Kingdom) Transition metal nitride/boride coatings have attracted attention in recent years owing to their high hardness, high temperature oxidation resistance and corrosion resistance, and Ti-B-N ternary films have been prepared by a wide variety of different techniques ¹. Although cubic boron nitride has many desirable properties, it is difficult to avoid producing, in part, the undesired hexagonal phase during PVD coating deposition. There is however an alternative approach, in that, with appropriate selection of composition, the BN phase can if required be almost completely suppressed, allowing coatings with primarily a nano-composite mixture of TiN/TiB₂ (i.e. TiBN_0.5) to be produced, which exhibits a desirable combination of high hardness (approaching that of c-BN), but with superior toughness, ref.1. It is not clear how the addition of aluminium to the Ti-B-N ternary system influences such nanocomposite behaviour, however there is some evidence to suggest that the aluminium will replace the Ti substitionally in primarily the TiN (rather than the TiB₂) phase ², and is unlikely to produce, for example, separate AlN, AlB_x or other AlB_xN_y phases. The inclusion of small but significant quantities of aluminium should lead to better high temperature oxidation performance in a similar way as has been reported for commercial TiAlN coatings (i.e. controlled Al₂O₃ layer formation), whilst also providing nanocomposite structure benefits. Titanium and aluminium inclusions within the B-N system have been reported in certain cases, to stabilise the cubic form of BN in deposited films ³, ⁴ but, in contrast, others suggest that the formation of undesirable h-BN is actually increased in this way, ref.2. Here we systematically study the influence of the chemical composition within a TiAlBN coating system deposited by a commercially available d.c. plasma-assisted electron beam PVD technique, and also by unbalanced magnetron sputtering, onto silicon wafers and AISI 316 stainless steel substrate materials. The composition of the films was determined by Auger Electron Spectroscopy and Glow Discharge Optical Emission Spectroscopy; chemical state information was gathered by X-ray Photoelectron Spectroscopy. Glancing-angle X-ray Diffraction was used to evaluate crystalline structure and peak shape parameters, whilst Scanning Electron Microscopy techniques were used to evaluate coating morphology and topography. Mechanical properties were evaluated by a variety of methods, including Knoop microhardness, Ultrasonic Surface Acoustic Waves (elastic modulus), Rockwell ‘C’ indentation and scratch adhesion, dry sliding pin-on-disc and reciprocating wear, ball-on-plate impact and abrasive wheel wear tests. Superior behaviour of the quaternary TiAlBN system over binary/ternary TiB₂ and TiBN coatings obtained by electron-beam PVD could be observed in dry sliding pin-on-disc and impact wear against WC balls ⁵; these effects are further examined with the modified set of coatings reported here. ¹W.Gissler, Structure and properties of Ti-B-N coatings, Surf. Coat. Technol., 68/69 (1994) 556-563. ²C.Mitterer, P.Rödhammer, H.Störi and F.Jeglitsch, Radio-frequency sputter deposition of boron nitride based thin films, J.Vac.Sci.Technol., A7 (1989) 2646-2651. ³Y.Doi, Sumitomo Electric Industries, Ltd., Japan Patent Laid Open No. 59-80775 (1 November 1982). ⁴H.A.Beale, Applied Coatings International, Inc., U.S. Patent No. 4412899 (1 November 1983). ⁵C.Rebholz, A.Ziegele, A.Leyland and A.Matthews, Structure, mechanical and tribological properties of TiAlBN electron-beam evaporated PVD hard coatings - submitted to Surf. Coat. Technol.
10:40 AM		TF+VM-TuM-8 Plasma Assisted Growth and Wear Behavior of Aluminum Oxynitride Thin Films. O.D. Greenwood, D.M. Marshall, S.D. Dvorak, R.J. Lad (University of Maine) Aluminum oxynitride (AlO_xN_y) films offer the possibility of hard protective and optical coatings which are stable at high temperature and humidity. The bulk mechanical properties of AlOxNy are known to vary strongly with composition and structure. We have synthesized AlO_xN_y films ranging in thickness from 10 to 500 nm on sapphire substrates using O₂ + N₂ ECR microwave plasma-assisted electron beam evaporation of aluminum and rf magnetron sputtering of aluminum nitride. The main parameters that were varied include deposition rate, N₂/O₂ gas flow ratio, substrate temperature and bias, and ECR plasma power. In-situ RHEED during growth indicates that epitaxial crystalline films can be produced at ~1073 K whereas polycrystalline or amorphous film growth occurs at lower temperatures. XPS and AES results indicate that N₂/O₂ gas flow ratios >>1 are required to incorporate equal amounts of oxygen and nitrogen into the evaporated films. XPS lineshape analysis is able to distinguish homogenous vs. phase separated microstructures. The dependence of tribological properties of the AlO_xN_y films upon surface stoichiometry and microstructure was quantified by friction and wear tests employing a range of slider diameters from nanometer to millimeter length scales. Results of single-pass and multiple-cycle scratch tests provide estimates of the critical stress for failure. Combined wear track topographical and chemical analyses help to elucidate the correlation between film microstructure and wear mechanisms.
11:00 AM		TF+VM-TuM-9 Effect of Temperature on Ti and TiN Films Deposited on BN Substrate S. Seal, J.H. Underwood (Lawrence Berkeley National Laboratory); M. Uda, H. Osawa, A. Kanai (Waseda University, Japan); T.L. Barr (University of Wisconsin, Milwaukee); E. Benko (The Institute of Metal Cutting, Poland); R.C. Perera (Lawrence Berkeley National Laboratory) Nitrides (such as BN, TiN) are widely used in various industrial applications because of their extreme wear and corrosion resistance, thermal and electronic properties. In the present case structural and chemical features formed during plasma vapor deposition (PVD) of Ti/TiN on BN substrates have been studied using synchrotron radiation near edge absorption spectroscopy (NEXAFS). Various phases of interest have been formed with different annealing temperatures. Diffusion of the nitridation and the interference from oxidation (e.g., TiO₂) and boride formation are of particular concern. Our NEXAFS data will be complemented by XPS and SIMS measurements.
11:20 AM		TF+VM-TuM-10 An XPS Study of N₂ Plasma Pretreatments on the Interface between Aluminum Alloy 7075-T6 and Films formed by Trimethylsilane Plasma Deposition. C.E. Moffitt, D.M. Wieliczka (University of Missouri, Kansas City); H.K. Yasuda (University of Missouri, Columbia) The interface region between the aluminum alloy 7075-T6 and films formed by D.C. anodic magnetron plasmas of trimethylsilane (TMS) and TMS + N₂ was investigated. These SiC-like films show promise as a corrosion protection coating which is deposited in a more environmentally benign fashion than currently used chromate conversion techniques. Alloy substrates exposed to various pretreatments and combinations of pretreatments, including alkaline cleaning and deoxidation, Ar + H₂ plasma sputtering, and N₂ plasma exposure, were examined with XPS to determine chemical state modifications to the alloy surface. TMS and TMS + N₂ plasma films deposited on similarly pretreated 7075-T6 substrates were then depth profiled with XPS in an effort to better understand the chemistry taking place at the plasma film-alloy interface. The authors would like to thank the United States Air Force and DARPA in their support through contract # F33615-96-C-5055.